Injection drug users (lDUs) have increased age-matched morbidity and mortality for both infectious and non-infectious medical conditions, associated with poverty, substance abuse and HlV/AlDS. This population has traditionally been considered 'difficult to reach.' Despite demonstrations of successful linkages of primary care to drug treatment programs, few models have been developed to meet the medical needs for active lDUs. Maintenance of contact with out-of-treatment lDUs have been possible through Needle Exchange Programs (NEPs). We propose to expand an innovative mobile health care program, The Community Health Care Van (CHCV), already linked to the New Haven NEP, to meet the special health needs of active IDUs. We will expand the hours of operation and provide an array of acute and preventive medical services, HlV -counseling and testing, social, drug treatment and case management services, and referral to traditional community-based health care institutions. These health services will principally target the needs of drug users with, or at high risk for, HlV infection; however, they will be available to all community residents. This research proposal combines health utilization, economic and sociobehavioral evaluation of this unique model of health services. We will measure the frequency and patterns of service utilization by all CHCV clients, the CHCV's ability to link clients to needed services, and compare the cost of providing NEP-based health services to those provided in an ER or hospital setting. We will study social and behavioral factors associated with utilization of health services in general, and specifically those health services associated with the CHCV. Lastly, we will enroll a cohort of 300 lDUs divided equally between CHCV user and non-users, in a one-year retrospective and 3-year prospective study of the economic consequences and impact of the CHCV on patterns and frequency of primary care and acute service utilization. We will study social and behavioral factors affecting utilization of medical, drug treatment, and social services among this cohort, with emphasis on issues relevant to the generalizability and reproducibility of this model of care. The project is favored by the setting of a relatively small city with high rates of drug use, a small network of closely linked sites of clinical care, NEP, and the broad resources of medical academic institution.